Ronald Gianotti

Continuous Non-contact Corneal Pachymetry with a High Speed Reflectometer

PURPOSE We developed an instrument that permits non-contact, continuous, high speed and high precision monitoring of corneal thickness and tested the stability and reproducibility of measurements made over extended time periods and under various conditions of low surface reflectivity encountered during protracted exposure of the unmoistened corneal surface to ambient air. METHODS The optical pachymeter (basic component of a broad-band, all-fiber Michelson interferometer) was used to monitor changes in the central corneal thickness of enucleated porcine eyes. Measurements were performed on three groups of eight eyes, each with different surface characteristics: intact epithelium, mechanically abraded epithelium, and 90 microm excimer laser keratectomy. Corneal thickness was monitored continuously with values recorded every 2 to 3 minutes for periods up to 1 hour in the absence of surface rinsing. RESULTS The thicknesses of all unmoistened corneas could be monitored with a precision of 1 microm (ascertained using a calibration glass plate and a living human cornea) over the entire observation period. Under ambient air conditions, deturgescence occurred in each case, and ranged from 1 to 5 microm/min. The rate of corneal thinning was fairly constant during the first 15 minutes of monitoring, but was nonlinear thereafter. Corneas with an intact epithelium had the lowest thinning rate with only 10% of the original thickness lost during the course of 1 hour. Deturgescence increased to 25% in corneas that had mechanical removal of the epithelium and to 28.5% in those that had an anterior excimer laser keratectomy, during a similar time-period. CONCLUSION With this new interferometric method, continuous, non-contact measurement of corneal thickness is possible to within a precision of 1 microm for periods up to 1 hour, even under the modified surface conditions after photoablative keratectomy. This device may be useful for on-line monitoring of ablation depths during such procedures.

Air-turbine driven optical low-coherence reflectometry at 28.6-kHz scan repetition rate

An optical low-coherence reflectometer is actuated with an air bearing turbine to show the feasibility of scanning at rates lying typically one order of magnitude above previously reported high-speed scanning systems. The rotation frequency of the air turbine of 427 000 rpm leads to a repetition rate of longitudinal scans of 28.6 kHz. Coherent signals are detected over a distance of 2 mm at a longitudinal scan speed of 175 m/s.

Rapid and Precise In Vivo Measurement of Human Corneal Thickness with Optical Low-Coherence Reflectometry in Normal Human Eyes

An optical low-coherence reflectometer is used for rapid noncontact measurements of the human corneal thickness in vivo. Thickness measurements on ten volunteers show a standard deviation of 3.4 μm. The experiments reveal that the optical reflectometer benefits from a 2.5 fold enhancement of the measurement precision and a 2.8 fold reduction in measurement time compared to a standard clinical ultrasonic pachometer.

Precision and Reproducibility of Measurements of Human Corneal Thickness with Rapid Optical Low-Coherence Reflectometry (OLCR)

This study investigates the precision and intraindividual variability of a clinical optical pachometer based on low-coherence reflectometry, which was used to measure the central thickness of a human cornea in vivo. The instrument, attached to a slit lamp, is a single mode fiber optic based Michelson interferometer with a high repetition rate as previously described. The same operator performed ten sets of measurements on the same subject, each consisting of 20 consecutive scans, on each day for three consecutive days. By computing the means from every scan series, the thickness of the central cornea with optical pachometry was found to be 519.6±1.2 (range 518-521) μm on day 1, 519.9±0.9 (range 519-521) μm on day 2, and 523.8±0.6 (range 523-525) μm on day 3. The thickness values on day 3, where the subject suffered from a cold without clinical ocular involvement, were different from the two previous days (p<0.001, one way analysis of variance). Optical low-coherence reflectometry measurements of corneal thickness can be performed with high precision of about 1 μm and a high intra- and intersession reproducibility.

Robust and rapid optical low-coherence reflectometer using a polygon mirror

A robust delay line comprising a rotated polygon mirror and a fixed glass parallelepiped is incorporated in an optical low-coherence reflectometer. A high degree of scalability of scan repetitiveness and scan range is obtained by producing the scan rate and scan range by means of a moving and a fixed element. The reflectometer is operated at a scan repetition rate and a scan speed of 2.58 kHz and 37 m/s, respectively.

Messung der Hornhautdicke bei der Photo-Keratektomie mit einem in den Strahlengang des Excimer-Lasers integrierten Reflektometer

Reference LOA-ARTICLE-1998-002doi:10.1055/s-2008-1034908View record in Web of Science Record created on 2009-01-20, modified on 2017-05-10

[Measuring corneal thickness in photo-keratectomy with a reflectometry incorporated into the laser beam of the excimer laser].

Reference LOA-ARTICLE-1998-002doi:10.1055/s-2008-1034908View record in Web of Science Record created on 2009-01-20, modified on 2017-05-10

Measurement of corneal thickness by low coherence reflectometry

Reference LOA-ARTICLE-1998-002doi:10.1055/s-2008-1034908View record in Web of Science Record created on 2009-01-20, modified on 2017-05-10